Wrapping material



Patented Aug. 13, 1935 UNITED STATES PATENT OFFICE.

2,011,246 wnarrmo MATERIAL William L. Hyden', Kenmore, N. Y., assignor to Du Pont Cellophane Company, Inc., New York, N. Y., a corporation of Delaware No Drawing. Application July Serial No. 621,315

5 Claims. (01. 9168) This invention relates to a means and method of minimizing the adhesionof contacting surfaces. The invention relates more particularly to preventing theharmful adhesion which occurs between sheets of thin, flexible, cellulosic material.

Regenerated cellulose pellicles are used for wrapping articles, for the fabrication of envelopes and similar articles and for these, and. for other, purposes are sometimes cut into sheets and stored in piles. These sheets, having smooth surfaces, substantially uniform gauge, and marked flexibility, come into intimate contact when stacked. Where the stacks are high and heavy or where pressure is applied to the pile,

The adhesion between sheets decreases the speed of handling the material in hand-wrapping, decreases the speed with which a wrapping machine can operate, interrupts the operation of automatic wrapping machines, and increases manufacturing costs.

A general object of the invention is to minimize the tendency of objects to adhere to one another. The particular object of the invention is to produce pellicles of thin flexible material which have little tendency to adhere to one another. Another object of the invention is to provide a method by which the tendency of pellicles to adhere can-be substantially overcome. Other objects of the invention will be in part apparent and in part set forth in this specification.

The objects of the invention are accomplished by applying to the pellicle an adhesive which is substantially imperceptible, non-tacky, and nonhygroscopic when dry. The objects of the invention are accomplished still. more particularly by the use of an adhesive of the protein class and by the specific substances and groups of substances herein disclosed.

The invention will be described with reference to wrapping sheets of regenerated cellulose but it is to be understood that it is applicable to all such materials.

In the practice of my invention I prefer to cast a regenerated cellulose pellicle after a known process and to pass it through a bath containing an adhesive which will be non-hygroscopic and substantially water-insoluble when dried. In

practice it is convenient to add the adhesive or size to the glycerine solution in the casting machine. It is also convenient to apply the coating to the dried pellicle after removal from the casting machine in a separate operation. 'If the latter procedure is adopted, it is advisable to incorporate enough glycerine or other softener in the sizing bath to prevent it from leaching glycerine or' other softener out of the pellicle.

The following are examples of my invention, but'neither the ingredients nor.the proportions thereof are limitative.

Example I A pellicle of regenerated cellulose is passed in the casting machine, after purification, through a bath containing the following materials and proportions:

I Parts by weight Light blood albumen about 0.35 Glycerine about 4.00 Formalin about 0.40 Waterout 95.25

The pellicle is then dried. During drying the formalin givesoifvapors of formaldehyde which act together with the heat to convert the albumen into a non-hygroscopic coating which is very diflicultly soluble in water. The formalin can be left out of this composition, the hardening of the albumen being carried out by heat alone or by treatment with formaldehyde vapors.

Example II About 11 parts by weight of casein are allowed to swell in about 44 parts by weight of water for at least thirty minutes. About one part by weight of ammonium hydroxide is then added, the temperature is slowly raised to about C. and about 44 parts by weight of water are stirred in, forming an emulsion of casein in water. This casein emulsion is made into a coating bath in the proportions of about 25 parts by weight of emulsion to about 4.5 parts by weight of glycerine and about 70.5 parts by weight of water. A cellulosic pellicle is run through this solution'at a speed which permits a treatment of from 20 to 60 seconds. Excellent results are obtained with the bath at any temperature around 25 C. to about C. The-pellicle is dried and is found to have a practically imperceptible non-hygroscopic coating which prevents adhesion.

The hardening of the casein may be advanced by the assistance of formaldehyde, ammonium dichromate, or other tanning agents.

Example III A sheet or film of undried regenerated cellulose or other cellulosic material is passed for approximately 20 seconds through a solution containing about 3 parts by weight of gelatine, about 4 parts by weight of glycerine, and about 93 parts by weight ofwater and is dried at a suitable temperature, for instance, at 95 or C. in 8. formaldehyde atmosphere.

The glycerine may be eliminated in the ba where the character of the pellicle or coating does not require its presence.

By means of my invention the objectionable tendency of cellulosic pellicles to adhere to each other is substantially eliminated. This elimination produces great advantages in economy of time in separating thin pellicles and improves the operation of wrapping machinery, without' affecting the transparency, flexibility, and other desirable properties of transparent stock. The invention may be used to reduce the adhesive tendency of other objects than those specifically herein mentioned.

The sizes listed above are dried, organic, nonhygroscopic substances, but the invention is not confined to organic materials. Inorganic adhesives which are substantially non-hygroscopic when dried are equally useful. An example of this class is water glass. Some advantage can be obtained with adhesives which have some hygroscopicity when use takes place in non-humid atmosphere, but for normal use non-hygroscopic adhesives are alone to be preferred.

The invention has been described in its application to regenerated cellulose pellicles in the form of flat sheets, but it is to be understood that it is equally applicable to cellulosic pellicles in rolls or other forms, to pellicles of other composition than regenerated cellulose such as cellulose esters and cellulose ethers, and to materials not in pellicle form which exhibit a tendency to adhere.

As many apparently widely different embodiments of this invention may be'made without departing from the spirit and scope thereof, it is to be understood that I do not limit'myself to the specific embodiments thereof except as defined in the appended claims.

I claim:

1. The method of minimizing the tendency of flexible, non-fibrous, cellulosic pellicles, having a thickness of the order of wrapping tissue, to adhere when stacked consisting in coating the pellicle with a substantially imperceptible protein layer, and insolubilizing and drying the protein coating.

2. The method of minimizing the tendency of flexible, non-fibrous, cellulosic pellicles, having a thickness of the order of wrapping tissue, to adhere when stacked consisting in coating the sheet with a substantially imperceptible albumin layer, and insolubilizing and drying the albumin coating.

3. The method of minimizing the tendency of flexible, non-fibrous, cellulosic pellicles, having a thickness of the order of wrapping tissue, to adhere when stacked consisting in coating the pellicle with a. substantially imperceptible gelatine layer, and insolubilizing and drying the gelatine coating.

4. The product of the process described in claim 1. I

5. The product of the process described in claim 2.

WILLIAM L. HYDEN. 

